1. Field of the invention
The present invention relates to a gas turbine engine compressor casing fitted with means for controlling its inner diameter so as to ensure a minimum objective radial clearance between the rotor and the stator of the compressor.
2. Summary of the prior art
Various solutions have been proposed for maintaining a radial clearance which is as small as possible between the rotor and the associated stator of a gas turbine engine compressor, and in particular between the tips of the movable blades and the inner wall of a casing surrounding the array of the blades, in order to ensure satisfactory performance of the engine in providing a good output and a low specific fuel consumption, while at the same time maintaining sufficient clearance to prevent any damaging mechanical interference between the stationary and rotating parts, particularly during transient acceleration or deceleration conditions and in whatever order they may occur. For example, the adjustment of clearances during operation may be achieved by making use of thermal means, particularly hot or cold air flows having adjustable flow rates depending upon specific operating parameters of the engine or upon direct measurements, these air flows usually being used to control the expansions or contractions of mechanical parts. Examples of such solutions are disclosed in French Pat. Nos. 2 534 982, 2 535 795 and 2 540 560.
In other solutions, mechanical means are used to vary the diameter of casings or stationary parts situated facing the rotors or rotating parts of a gas turbine engine. Examples of such arrangements are disclosed in French Pat. Nos. 2 577 282 and 2 591 674.
However, these known solutions are not entirely satisfactory in all applications. The taking of air, often in relatively substantial amounts, required by implementing solutions using thermal means causes the engine performance to lose a not insignificant part of the contribution made by these arrangements. The mechanical means envisaged have the drawback of increasing the mass of the engine, which is particularly disadvantageous for aeronautical applications, and of requiring complicated assemblies. In particular, the implementation of the known solutions is found to be delicate and difficult to achieve in the application to gas turbine engine compressors with casings formed by two half-shells joined together by flanges.